1. Field of the Invention
The present invention relates to rotating electric machines such as synchronous machines. It also relates to double-fed machines, applications in asynchronous static current converter cascades, external pole machines and synchronous flux machines, as well as to alternating current machines intended primarily as generators in a power station for generating electric power. The invention particularly relates to the stator in such machines and a method for fixing the windings, as well as cooling the stator teeth and the insulated electric conductor constituting the stator winding.
2. Discussion of the Background
Similar machines have conventionally been designed for voltages in the range 15-30 kV, and 30 kV has normally been considered to be an upper limit. This generally means that a generator must be connected to the power network via a transformer which steps up the voltage to the level of the power network, which is in the range of approximately 130-400 kV. The present invention is intended primarily for use with high voltages. High voltages shall be understood here to mean voltages in excess of 10 kV. A typical operating range for the machine according to the invention may be voltages from 36 kV up to 800 kV. The invention is secondarily intended for use in the stated technical area at voltages below 36 kV.
Two different air-cooled systems exist for conventional cooling: radial cooling where the air passes the rotor through the hub and radial channels in the rotor, and axial cooling where the air is blown into the pole gaps by axial fans. The stator is divided into radial air ducts created by (often straight) spacers that are welded in place. Due to the poor thermal conductivity axially through the stator laminations the air ducts must be frequently repeated. The drawback with air-cooling is that the ventilation losses are considerable and that, because of the ventilation ducts, the stator becomes longer. Furthermore, particularly with said high-voltage generators with long teeth, the ventilation ducts may also weaken the structure mechanically.
Axial liquid cooling, e.g. water-cooling, through cooling tubes, e.g. of metal, in the stator yoke has been known for some time. One drawback is that eddy currents are induced in metal tubes if they are present in a magnetic flux varying with time, thus leading to certain power losses when used in an electric machine.